High PV Penetration Research Articles

Optimal Discrete Net-Load Balancing in Smart Grids with High PV Penetration

Mitigating supply-demand mismatch is critical for smooth power grid operation. Traditionally, load curtailment techniques such as demand response have been used for this purpose. However, these cannot be the only component of a net-load balancing framework for smart grids with high PV penetration. These grids sometimes exhibit supply surplus, causing overvoltages. Currently, these are mitigated using voltage manipulation techniques such as Volt-Var Optimizations, which are computationally expensive, thereby increasing the complexity of grid operations. Taking advantage of recent technological developments that enable rapid selective connection of PV modules of an installation to the grid, we develop a unified net-load balancing framework that performs both load and solar curtailment. We show that when the available curtailment values are discrete, this problem is NP-hard and we develop bounded approximation algorithms. Our algorithms produce fast solutions, given the tight timing constraints required for grid operation, while ensuring that practical constraints such as fairness, network capacity limits, and so forth are satisfied. We also develop an online algorithm that performs net-load balancing using only data available for the current interval. Using both theoretical analysis and practical evaluations, we show that our net-load balancing algorithms provide solutions that are close to optimal in a small amount of time.

High PV Penetration Impact on European-based LV Residential Network

The impact of high PV penetration into the grid particularly at the distribution side has been extensively studied. However, most of the available research focuses on North American style systems. This project aims to investigate the effect of high PV penetration at a residential area in a European-based distribution network, which is electricity supply system Malaysia is based on. The modeling is done using OpenDSS while the network model used is the IEEE European Low Voltage Test Feeder which consists of 55 loads representing a generic housing area. Each load point is then equipped with a 4 kW PV system-representing a typical size for a house installation. PV output variability is then introduced into the modeling using two sample days of actual irradiance variability obtained from UTeM Malaysia; one for clear day and another for a high variability day. Voltage unbalance, voltage rise and reverse power flow were analyzed. One significant finding of this project is that voltage rise exceeds the standard of 1.05 pu during noon. Besides that, the high variability days significantly affect the mitigation measures required to manage reverse power flow.

A review of balancing costs in Italy before and after RES introduction

The massive introduction of RES in electricity markets is recognized to have induced a merit order effect on wholesale prices. While day-ahead prices are likely to decline as RES-E production increases, the effects on balancing market sessions are more ambiguous. Taking into account the Northern Italian zone characterized by a high solar PV and hydro penetration, we provide empirical evidence that balancing quantities decreased while costs increased between two samples associated with low (2006–08) and high (2013–15) RES levels. We estimate balancing costs for different technologies and compare their dynamics across specific hours. We find evidence of increasing balancing prices in particular market conditions, that we interpret as a signal of strategic use of real time sessions by conventional producers prone to the merit order effect in the day-ahead market. We compare our results to those obtained in the German market (where, on the contrary, balancing costs have decreased) and postulate that the different market designs may explain these results. Our findings suggest that the Italian policy makers should carefully monitor all trading sessions, especially those close to real time, to avoid the exercise of market power by few operators allowed to guarantee system security and, additionally, to promptly adopt a capacity market.

A simulation framework for assessing the market and grid driven value of flexibility options in distribution grids

The increasing share of renewable distributed energy resources (DERs) entails a rising number of congestions in the German distribution grids, such as voltage band violations and overloading of network assets. Consequently the need for grid expansion increases [1]. A politically promoted alternative to grid expansion is managing congestions by the preventive use of flexibility options, such as flexible generation, load management and storage systems [2]. However, preventive congestion management is not yet established in distribution grids. Thus, various measures are under discussion to stimulate the provision of flexibility options by its owners for concerns of congestion management. Assessing the suitability of solutions among these congestion management measures (CMMs) requires a realistic modeling of grid operation, energy system structures and the behavior of the owners of DER and flexibility options.The intended application of the presented simulation framework is consequently the assessment of the macro- and micro-economic effects of preventative CMMs in distribution grids. Supporting that goal, the design of an agent-based simulation framework, which incorporates detailed optimization models for simulating the behavior of grid users (owners of DER and flexibility options) and Distribution System Operators (DSO) is presented. Exemplarily it is applied on a realistic distribution grid use case. The simulation framework enables analyzing the consequences of the grid users’ interaction with the DSO following defined CMMs. Within the framework, the grid users are modeled as individually or market driven oriented users, who both aim at improving their micro-economic situation. The DSO’s operational target is the minimization of congestion management costs under application of several CMMs.The exemplary application focuses on four congestion management concepts, such as flexible tariffs and a market-based flexibility provision. The chosen use case comprises a congested distribution grid with high PV penetration and grid users at the medium and low voltage level. In the use case, the alternatively necessary curtailment of renewable energy can be reduced from 15% to 35% depending on the considered CMM. The most promising CMM (a market-based flexibility provision) reduces the DSO’s congestion management costs by 33%, without degrading the grid users’ economic situation. Future work will advance the analyses based on a comprehensive database of realistic distribution grid scenarios.

Techno-economic analysis of battery storage and curtailment in a distribution grid with high PV penetration

Global solar PV capacity continues growing and this technology is a central solution for the global energy transition based on both economic growth and decarbonisation. PV technology is mainly being installed in distribution networks next to the consumption centres but it is an intermittent source which does not offer demand matching capability therefore calling for the redesign of distribution networks. In this study, battery storage and PV curtailment are compared as solutions for a residential area in Zurich (Switzerland) with large PV penetration from a techno-economic perspective. The techno-economic analysis focuses on the implications of the location (and related size) of battery storage and the type of curtailment control (fixed versus dynamic) for relevant stakeholders such as consumers and the distribution network operator. PV energy time-shift, the avoidance of PV curtailment and the upgrade deferral of the distribution transformer are the energy services provided by battery systems. Residential batteries offer more value for PV management than grid-scale solutions despite higher levelized cost but PV curtailment is the most cost-effective solution since only up to 3.2% of total PV electricity generation in energy terms should be curtailed for avoiding the transformer upgrading. We conclude that shared ownership models for PV curtailment could considerably improve its acceptance among consumers.

Overcurrent Protection Assessment with high PV Penetration in a Distribution Network

The utilization of DGs has revolutionized power utility and has recently promoted renewable energy technology with considerable positive impacts such as loss-reduction, reliability improvement of grids, economic benefits and ecological preservation progress. Solar energy, considered as one of the cleanest energy in the energy industry, is becoming an indispensable and strategic need in Power Supply. PV integration to grid brings new challenges, thus technical issues influencing the entire Network. To guarantee a stable and safe grid energy supply, some aspects have to be taken into consideration preventing partial or total unnecessary outage. This can be done only through the implementation of an efficient and effective control and protection mechanism as DGs are known to have impacts on distribution over current protection system. This paper investigated the potential protection issues associated to high PV penetration. The impact of different penetration level (20%, 40% and 60%) on two different network configurations (centralized and distributed) which have been modeled and analyzed using PSCAD/EMTDC software. The inverter controller response was assessed under grid faults integrating LVRT capabilities. The presence of PVs in the grid has led to identify nuisance tripping or false tripping in high penetration condition of Solar PV. Moreover, and most important presented in this research is the operational impacts study of PVs on the protection coordination which has been done for a satisfied backup and selectivity protection with a reliable and effective relay setting suggestion. Some measures have been recommended as well to mitigate the PV impacts with an acceptable penetration level.

Impact of large scale PV deployment in the sizing of urban distribution transformers

Abstract With the increasing deployment of solar systems in buildings in urban environments, a future scenario of high photovoltaic penetration is expected to produce impacts on the distribution grid. One of the challenges relates to the power balance at the power transformers, which might not have sufficient spare capacity to accommodate the solar electricity feed in. In this work, we estimate the power balance at the transformers in a small urban area of Lisbon, Portugal, considering full deployment of PV, installed on rooftops and building facades. The PV potential is estimated through two different approaches: the simplified Peak power method, which considers the typical peak power of a module and the available area, and the more labour-intensive Irradiance method that accounts for hourly time step solar irradiance and demand data or simulations. The main findings of this work point out that the Peak power method has limited success if PV facades are to be considered. Moreover, a high PV penetration scenario leads to a locally less resilient grid, hence a solar PV factor was proposed to account for future deployment of PV systems in urban environments.

A Strategic Approach Using Representative LV Networks in the Assessment of Technical Losses on LV Network with Solar Photovoltaic

Low voltage network (LVN) forms an extensive part of the distribution network as it is used to connect electricity supply from utility substations to diverse segments of loads in different geographic locations. With the increasingly high penetration of solar PV in LVN, utility companies are finding it necessary to establish the contribution of these solar PV to the overall technical losses in the distribution network. This paper presents a strategic approach using representative LVN to determine the impact of solar PV on technical losses on the LVN. Five types of representative LVN characterized by different customer load segments (domestic, commercial and industrial) and peak load demand were developed. The impact on technical losses of solar PV connected to these representatives LVN were assessed on a statistical basis for a supply zone. The results obtained are consistent and could be applied to establish investment strategies on distribution network, tariff revision exercise and optimization of distribution network planning/design.

Techno-economic assessment of forecasting and communication on centralized voltage control with high PV penetration

The current increase of solar generation in the power system, especially at low-voltage (LV) and medium-voltage (MV) levels, poses a great challenge from the distribution system operation point of view. Centralized voltage control schemes have been presented in the literature as a promising solution to deal with the voltage violations that may be caused by these high solar PV penetration levels. However, this approach relies on the accuracy of forecasted data to optimize the set-points and on the effectiveness of communication infrastructures to send them from the central unit to the inverters at the PV panels. This article presents a novel methodology developed in the European project SUSTAINABLE to assess the impact of forecasting and communication on centralized voltage control. This methodology has been applied trough simulation in two Portuguese networks used for the demonstration activities of the project, one in LV and another in MV. The results show that the accuracy of the data used to calculate the set-points as well as the time interval used for their transmission have a significant impact in these applications and highlight the importance of dedicating resources to improve both forecasting tools and communication systems.

INVESTIGATION WITH MODAL ANALYSIS OF EFFECTS OF HIGH PV PENETRATION ON POWER SYSTEM VOLTAGE STABILITY

This paper shows the effects of high PV integration on the power system voltage stability. PV power plant was applied to the IEEE 30 bus test system. Modal analysis method is used to show the effect of PV integration on power system voltage stability. The power rate of synchronous generator in the IEEE 30 bus system is increased to show the power system stability effect of high PV penetration and then the PV generation with the same power rate is connected appropriate bus in power system. The modal analyses of systems are done without any PV generation and with collective and scattered PV generation at various rates. In PV penetration, two scenarios, namely collective and scattered are examined. The results obtained showed that the increased penetration of PV system affects the power system voltage stability positively.

Distributed control of thermostatically controlled loads in distribution network with high penetration of solar PV

High penetration of solar energy can result in voltage rise in midday, while growth in residential air conditioning is the main contributor of overloading and voltage drop issues during peak demand time. This paper provides a hierarchical control scheme to coordinate multiple groups of aggregated thermostatically controlled loads to regulate network loading and voltage in a distribution network. Considering the limited number of messages that can be exchanged in a realistic communication environment, an event-triggered distributed control strategy is proposed in this paper. Through intermittent on and off toggling of air conditioners, the required active power adjustment is shared among participating aggregators to solve the issue. A case study is conducted and simulation results are presented to demonstrate the performance of the proposed control scheme.

Design of Special Protection System for an Offshore Island With High-PV Penetration

An intelligent load-shedding strategy was designed and embedded in the special protection system (SPS) to enhance the system stability for an offshore island with high penetration of photovoltaic (PV) systems. To prepare the training data set for the artificial neural network (ANN), the transient stability analysis of the isolated power system was executed to determine the minimum amount of load to be interrupted to prevent the tripping of diesel generators for the emergency shutdown of PV systems. By selecting various combinations of PV penetration levels, total system load demand and the frequency decay rate at the instant of PV system tripping as the input neurons of the ANN, the proper load shedding scheme is derived and stored in the decision knowledge base of the SPS. When the intelligent energy management system (iEMS) detects the tripping of PV system, the SPS will be triggered to determine the amount of loss to be disconnected and executes the corresponding load interruption. By applying the proposed ANN based load shedding scheme in SPS, the amount of customer loading to be interrupted has been reduced dramatically for the restoration of system stability after the emergency shutdown of high penetration PV system.

The Res-Induced Switching Effect Across Fossil Fuels: An Analysis of the Italian Day- Ahead and Balancing Prices and Their Connected Costs

The massive introduction of RES in electricity markets has influenced the long-run dynamics of electricity prices and their interactions with conventional thermal production sources. Taking into account the Northern Italian zone characterized by a high solar PV and hydro penetration, we firstly provide empirical evidence on the fuels-electricity nexus across two samples characterized by low (2006-08) and high (2013-15) RES levels, both in the day-ahead and balancing markets. Then, we estimate the costs for balancing power disentangling for technologies and comparing their dynamics across specific hours in both samples. We show that the fuels-electricity nexus has changed significantly in the day-ahead sessions and selectively in the balancing sessions. We also find evidence of high balancing prices that we interpret as a signal of strategic use of real time sessions by conventional producers. Our findings suggest policy makers to carefully monitor all trading sessions, especially those close to real time, to avoid the exercise of market power by few operators allowed to guarantee system security and to promptly adopt a capacity market.

Very short term load forecasting of a distribution system with high PV penetration

A battery energy storage system (BESS) is an available solution for utilities to deal with intermittency issues resulting from renewable energy resources. A BESS needs to have a control algorithm to provide a very good estimation of the load on the grid at each time step. A short-term load forecast (STLF) is necessary for efficient and optimized control of BESSs that are connected to the grid. In this work, two parallel-series techniques for load forecasting are proposed to optimize the performance of a grid-scale BESS (1 MW, 1.1 kWh) in 15-min steps within a moving 24-h window. In both techniques, a complex-valued neural network (CVNN) is used for parallel forecasting. The parallel component is based on the search for similar days of historical data that have a weekly index comparable to the forecast day. For series forecasting, historical data of each day is used within a moving forecast window by CVNN along with the spline method. For both techniques, parallel forecasting is mixed with series forecasting by an adjustment coefficient. Both techniques are tested on a set of real data for a grid with high PV penetration, and the obtained results are compared.

Impact of High PV Penetration on the Inter-Area Oscillations in the U.S. Eastern Interconnection

This study explores the impact of high PV penetration on the inter-area oscillation modes of large-scale power grids. A series of dynamic models with various PV penetration levels are developed based on a detailed model representing the U.S. Eastern Interconnection (EI). Transient simulations are performed to investigate the change of inter-area oscillation modes with PV penetration. The impact of PV control strategies and parameter settings on inter-area oscillations is studied. This study finds that as PV increases, the damping of the dominant oscillation mode decreases monotonically. It is also observed that the mode shape varies with the PV control strategy and new oscillation modes may emerge under inappropriate parameter settings in PV plant controls.

出力予測を考慮した発電機起動停止計画モデルによる太陽光発電出力制御必要量の分析

High penetration of variable renewable energy (VRE) systems will impact power system operations because generation of VRE systems depends on weather conditions. We analyzed the operational situation and photovoltaic power yield curtailment for the Tokyo Electric Power Company area in 2030 using day-ahead unit commitment (UC) model when a high penetration of VRE systems is expected. At first, we updated our UC model to optimize PV curtailment keeping power system's security (load frequency control reserve) and minimizing operational cost. Using the updated model, we found that in case of 53GW and 100GW of PV penetration, around 0.34% and 4.83% of PV curtailment would be required throughout the year. High curtailment rate would be required only in spring and autumn seasons when power demand is small and PV yield is large. Regarding the other seasons, high curtailment rate would not be needed in any of the high PV penetration scenarios.

Achieving very high PV penetration – The need for an effective electricity remuneration framework and a central role for grid operators

This article proposes that optimally deployed solutions to the intermittency introduced by high penetration solar – e. g., electrical storage, optimized curtailment and demand response – could affordably transform solar power generation into the firm power delivery system modern energy economies require, thereby enabling very high solar penetration and the displacement of conventional power generation. The optimal deployment of these high-penetration-enabling solutions imply the existence of a healthy power grid, and therefore imply a central role for utilities and grid operators.This article also proposes that a value-based electricity compensation mechanism (based on e.g., Value of Solar (VOS) and load shaping tariffs), recognizing the multi-facetted, penetration-dependent value and cost of solar energy, and capable of shaping consumption patterns to optimally match resource and demand, could be an effective vehicle to enable high solar penetration and deliver affordable firm power generation.

High Penetration PV in Distribution Networks, Design and Control

<p>Global warming is a direct consequence of consumption of fossil fuels which emit greenhouse gasses as they produce energy. Solar energy is the most available energy throughout the world in which regardless of capital investment is free and most importantly clean and emission free and could be a solution for global warming along with other renewable sources of energy. But as photovoltaic energy is becoming widespread and penetration level of photovoltaic power plants increase, several issues rise in distribution networks. In this paper, a high penetration photovoltaic power plant is designed and issues associated with it are thoroughly discussed. Voltage rise and cloud passage effect are amongst the most challenging issues in design and implementation of a high penetration photovoltaic power plant in distribution networks. Transient effects of cloud passage could lead to unacceptably low voltage in Point of Common Coupling and maximum penetration level must be set according to these issues. An efficient Maximum Power Point Tracking (MPPT) and a DC link voltage control scheme are also presented. Simulations have been done in Matlab/Simulink environment.</p>

An approach for assessing high-penetration PV impact on distribution feeders

The variability of solar power due to cloud shadows with high penetration levels can cause technical issues such as power fluctuation and voltage flicker in power distribution feeders. To help distribution planners better understand and predict these likely impacts on voltage quality and avoid overly conservative decisions on the amount of PV installed on a feeder, a comprehensive simulation method is needed to model and address these problems. To this end, this paper presents a simulation and analysis approach that uses a cloud shadow model to recreate the variable output power of both distributed and large centralized PVs at various locations on a feeder. Simulations are made on an actual EPRI test feeder. EPRI's OpenDSS distribution simulation program is driven through MATLAB. The feeder is monitored at all buses, and PV induced voltage quality issues are measured, including the dynamic reaction of voltage control devices. The example feeder illustrates the usefulness of the new evaluation method to address and quantify impacts of large amounts of PV systems on feeder steady-state over voltage, voltage fluctuation level and flicker, and voltage regulation device operation. Results for distributed PV show that PV levels as high as 50% can be tolerated.

空間平均日射強度のランプ変動時における短周期変動特性

Sudden and large changes in renewable energy generators called ramp events are one of the major issues to be addressed for the stable operation of electric power system. By classifying the change of spatial average irradiance in a day, which is the primary factor of aggregated power output of photovoltaic power generation system (PV system), this study statistically evaluated the frequency of ramp events in a year. As a result for the spatial average irradiance in the Chubu area in Japan, the ramp event occurs in 42 days (12%) in a year. The duration of ramp event varies mainly between 30-120min. Then, this study statistically evaluated the short-cycle fluctuation characteristics of spatial average irradiance during ramp event. As a result, in the case of ramp down of relatively large width, the short-cycle fluctuation before and during the ramp event is as large as that in quasi-fine day, while it after the ramp event is small enough as in cloudy day. The results can be useful as approximate evaluation regarding generation flexibility required in electric power system with high penetration PV systems.